Partial Unicompartmental System for Partial Knee Replacement

ABSTRACT

A prosthetic system for use as a partial unicompartmental artificial knee replacement system. In one form, an artificial femoral bearing component is implanted along with a floating meniscus component that is configured to cooperate with the femoral bearing component to move through a plurality of translational and rotational positions as the knee rotates through a variety of angles. In another form, an artificial tibial bearing component is implanted along with a floating meniscus component that is configured to cooperate with the tibial bearing component to move through a plurality of translational and rotational positions as the knee rotates through a variety of angles.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.15/003,482, filed Jan. 21, 2016, now U.S. Pat. No. 9,867,709, whichclaims priority to U.S. Provisional Application No. 62/106,091, filedJan. 21, 2015, each of which is hereby incorporated by reference in itsentirety.

BACKGROUND

The present disclosure generally relates to medical prosthetic devices,systems, and methods. More specifically, in some instances the presentdisclosure relates to prosthetic devices that replace at least part ofthe functionality of the natural meniscus and knee bearing surfaces.Each knee has two menisci, a lateral meniscus and a medial meniscus.Each meniscus is a crescent-shaped fibrocartilaginous tissue attached tothe tibia at an anterior and a posterior horn. Damage to the meniscuscan cause pain and arthritis. Further, cartilage on the bearing surfacesof the tibia and femur may also become damaged, leading to additionalpain and damage to the meniscus. Accordingly, it is current practice toperform a total knee replacement in many patients with damaged kneecartilage. Alternatively, if the damaged cartilage is limited to oneside of the knee, a unicompartmental knee replacement procedure may beperformed where the femur and tibial bones are milled off and implantsare inserted into both bones to perform the bearing function of theknee. Even if cartilage of only one of the bone surfaces is damaged,both cartilage surfaces will be removed and replaced with an artificialbearing surface.

There remains a need for less traumatic and bone sparing devices thatcan accomplish load bearing and knee function through a range of kneemotions. While existing devices, systems, and methods have attempted toaddress these issues, they have not been satisfactory in all respects.Accordingly, there is a need for the improved devices, systems, andmethods in accordance with the present disclosure.

SUMMARY

In one embodiment, a partial unicompartmental knee replacement system isprovided. The partial unicompartmental knee replacement system offers asystem to allow treatment of only the effected joint surface whileretaining the intact cartilage bearing surfaces on the opposing portionsof the joint. In one form, the system includes a femoral componentconfigured for resurfacing at least a portion of a femoral condyle, thefemoral component having a first bearing surface with a first radius ofcurvature, a second bearing surface with a second radius of curvatureand a third bearing surface with a third radius of curvature and ameniscus component, configured for placement between the femoralcomponent and the natural tibia. The meniscus component floats in theknee joint between the natural tibia and the femoral component and has afirst position in the knee joint when in contact with the first area, asecond position in the knee joint when in contact with the second areaand a third position in the knee joint when in contact with the thirdarea. In one aspect, the first position is rotationally offset from atleast one of the second and third positions. In a further aspect, thefirst position is longitudinally offset from at least one of the secondand third positions. In still a further aspect, the first position islaterally offset from at least one of the second and third positions. Inat least one form, the first radius of curvature is different than thethird radius of curvature.

In a further form, a tibial bearing component may be implanted toreplace the natural tibial bearing surface. The tibial bearing componentincludes a multi-faceted bearing surface with a convex bearing portion.A free floating meniscus device has a lower surface for engaging thetibial bearing component and an upper surface for engaging the naturalfemoral bearing surface. The meniscus device floats between a pluralityof anterior to posterior, and rotational positions, in response tomovement of the femur and engagement with the multi-faceted bearingsurface of the tibial bearing component.

In another embodiment, a method is provided for replacing the functionof a cartilage bearing surface and a meniscus within a joint. The methodof replacing the bearing surface includes removing the cartilage surfacefrom one bone in the joint and implanting a replacement bearingcomponent. The method of replacing the meniscus function within a jointincludes removing a portion of a meniscus within the joint and leavingintact a meniscus remnant, then inserting a free floating meniscusreplacement implant into the joint and engaging the meniscus replacementimplant with the meniscus remnant such that the meniscus replacementimplant is at least in part retained within the joint by the meniscusremnant. In a further aspect, the meniscus replacement implant includesa retention channel within the sidewall of the implant and the method ofengaging the meniscus replacement implant with the meniscus remnantincludes aligning the retention channel with the meniscus remnant. Instill a further feature, the retention channel is a retention channelformed in a posterior portion of a knee meniscus replacement implant andthe engaging includes aligning the retention channel with a posteriorportion of the meniscus remnant. In yet a further aspect, the engagingincludes suturing a portion of the meniscus replacement implant to aportion of the meniscus remnant or to tissue of the joint capsuleadjacent the joint.

BRIEF DESCRIPTION OF DRAWINGS

Other features and advantages of the present disclosure will becomeapparent in the following detailed description of embodiments of thedisclosure with reference to the accompanying of drawings, of which:

FIG. 1 is a diagrammatic perspective view of a right knee joint with aunicompartmental knee replacement according to one aspect of the presentinvention.

FIG. 2 is a diagrammatic partially exploded perspective view of a leftknee joint with a unicompartmental knee replacement according to oneaspect of the present invention.

FIG. 3 is a side view of a femoral bearing component.

FIG. 4 is a diagrammatic perspective view of an alternative femoralbearing component.

FIG. 5 is a front view of a partial unicompartmental knee replacementsystem according to one embodiment.

FIG. 6 is a perspective view of a prosthetic meniscus component.

FIG. 7 is a cross section of the meniscus component of FIG. 6.

FIG. 8 is a perspective view of a knee illustrating an implantedmeniscus device in a series of positions.

FIGS. 9A-9C illustrate an implanted partial unicompartmental kneereplacement system according to the present invention with the kneearticulated through a series of angles.

FIGS. 10A-10C illustrate the rotational position of the meniscuscomponent of the system in FIGS. 9A-9C.

FIGS. 11A and 11B illustrate a meniscus device with tethering loops.

FIGS. 12A-12C are diagrammatic illustrations of a prosthetic partialunicompartmental knee replacement system of a further embodimentassociated with the knee joint.

FIGS. 13A-13C illustrate various views of the system of FIG. 12A.

FIGS. 14A-15C illustrate various views of the tibial plateau bearingcomponent associated with the system of FIG. 12A.

FIGS. 16A-16D illustrate an implanted partial unicompartmental kneereplacement system according to FIG. 12A with the knee articulatedthrough a series of angles.

FIGS. 17A-17C illustrate the rotational position of the meniscuscomponent of the system shown in FIGS. 16A-16D.

DETAILED DESCRIPTION

For the purposes of promoting an understanding of the principles of thepresent disclosure, reference will now be made to the embodimentsillustrated in the drawings, and specific language will be used todescribe the illustrated embodiments. It is nevertheless understood thatno limitation of the scope of the disclosure is intended. Any and allalterations or modifications to the described devices, instruments,and/or methods, as well as any further application of the principles ofthe present disclosure that would be apparent to one skilled in the artare encompassed by the present disclosure even if not explicitlydiscussed herein. Further, it is fully contemplated that the features,components, and/or steps described with respect to one embodiment may becombined with the features, components, and/or steps described withrespect to other embodiments of the present disclosure.

Referring now to FIG. 1, there is shown a right knee joint between femurF and tibia T. A partial unicompartmental knee replacement (PUKR) system100 has been implanted in the medial compartment of the knee. As will beexplained in greater detail below, the PUKR system is only a partialunicompartmental knee replacement as it leaves intact at least one ofthe natural bearing surfaces of the knee. In the illustrated embodiment,an artificial femoral bearing surface 120 has been implanted on thefemur to bear against a prosthetic meniscus device 110, which in turnbears against the native tibial plateau. A superior surface of theprosthetic meniscus device 110 is in contact with the artificial femoralbearing surface 120, and an inferior surface of the prosthetic meniscusdevice 110 is in contact with the natural tibial bearing surface. FIG. 2illustrates that a similar system may be implanted in the left knee,including the prosthetic meniscus device 110 and the femoral bearingsurface 120. The meniscus device 110 is positioned within the knee jointadjacent to a ligament 130, such as a coronary or meniscotibialligament, a meniscofemoral ligament, and/or a transverse ligament. Forillustrative purposes, the prosthetic system will be described in thefollowing drawings in conjunction with a left knee, medial meniscus andbearing surface replacement. However, corresponding embodiments areutilized for replacement of any of the other knee bearing surfaces andmenisci, such as the right knee medial meniscus, left knee lateralmeniscus, and/or right knee lateral meniscus. In that regard, the size,shape, thickness, material properties, and/or other properties of theprosthetic device may be configured for each particular application.

FIG. 3 illustrates a femoral bearing component 120. The femoral bearingcomponent includes a first bearing area 310 having a first largerradius, a second bearing area 312 having a second radius smaller thanthe first, and a third bearing area 314 having a third radius smallerthan the second radius, and a fourth bearing surface 316. Although amulti-radii femoral component is shown, it is possible that the femoralcomponent can have a bearing surface with a single continuous bearingsurface having a single radius or a number of radii less than or greaterthan the four shown in FIG. 3. In that regard, the one or radii of thefemoral bearing component 120 can be selected to mimic the shape of anatural femur. The femoral bearing surface is held in place in the boneby insertion of the posts 330 and 332 into prepared bone holes. Whiletwo posts are shown, it will be appreciated that any number of anchoringextensions on the back side of the femoral component can be utilized toobtain a solid anchorage to the bone. The femoral component 120 replacesthe patient femoral bearing surface on the side of the knee where it isused. For example, the femoral component 120 can be implanted to remedya defect of either the medial condyle or the lateral condyle. Analternative femoral bearing component 350 is shown in FIG. 4. Femoralbearing component 350 has a smaller bearing surface that is intended toreplace a relatively small defect in the natural femoral bearing surfacesuch that surface 352 mimics the patient's bearing surface naturalshape. As shown in FIG. 5, the femoral component 350 may be implantedinto the knee using post 356 to retain its position along with acorresponding prosthetic meniscus device according to the presentdisclosure. The femoral component may be formed of any suitablebiocompatible material, including but not limited to, cobalt chrome.

Referring now to FIGS. 6 and 7 shown therein is a prosthetic devicehaving features similar to a prior design set forth in U.S. Pat. No.8,361,147, which is hereby incorporated by reference in its entirety.Generally, the prosthetic device is for the replacement of the functiona meniscus in a partial unicompartmental knee replacement system and isconfigured to interact with the replacement bearing surface to move themeniscus component to different engagement positions with opposingnatural bearing surface. The prosthetic meniscus can be implanted toreplace the lateral meniscus or the medial meniscus. In that regard, aprosthetic lateral meniscus is disposed between and in contact with anartificial lateral femoral bearing surface and the natural lateraltibial plateau. Similarly, a prosthetic medial meniscus is disposedbetween and in contact with an artificial medial femoral bearing surfaceand the natural medial tibial plateau. As described below, theprosthetic meniscus device can also be utilized with a natural femoralbearing surface and an artificial tibial bearing surface. The mobilityof the meniscus device mimics a natural meniscus and distributes theloading stresses more naturally to the remaining natural bearing surfacewhen utilized with a partial unicompartmental knee replacement system.The meniscus device is sized to interact with a specifically sizedprosthetic femoral component. Thus, it is contemplated that the femoralcomponent is matched to at least one meniscus device and that multiplematched pairs of implants will be available to treat patients withdifferent knee anatomies and sizes.

The prosthetic meniscus comprises an outer body portion 108 and acentral body portion 110. Generally, the outer body portion 108 has anincreased thickness and height relative to the central body portion 110.In some instances the outer body portion 108 has a thickness between 5mm and 15 mm. In some instances, the central body portion 110 has athickness between 0.5 mm and 5 mm. In one particular embodiment, theouter body portion 108 has a maximum thickness of approximately 10 mmand the central body portion 110 has a maximum thickness ofapproximately 2 mm. The height or thickness of the outer body portion108 varies around the perimeter of the prosthetic device in someinstances. In that regard, the variations in the height or thickness ofthe outer body portion 108 are selected to match the anatomical featuresof the patient in some embodiments. Similarly, the height or thicknessof the central body portion 110 varies across the prosthetic device insome embodiments. Again, the variations in the height or thickness ofthe central body portion 110 are selected to match the anatomicalfeatures of the patient in some embodiments. In some embodiments, theprosthetic device 100 is inserted in an insertion configuration and thenloaded, stretched, moved, and/or otherwise transferred to animplantation configuration. In some embodiments the transformationbetween the insertion configuration and the implantation configurationis facilitated through the loading of the prosthetic device 100. In suchembodiments, the variations in height or thickness of the outer andcentral body portions 108, 110 are selected to accommodate thedeformation or transformation between the insertion configuration andthe implantation configuration.

In the illustrated embodiment, the prosthetic device is configured foruse without a fixation member or fixation device that would penetrate anadjacent bone and/or soft tissue to keep the prosthetic device in place.Rather, the prosthetic device 100 is configured to “float” within theknee joint without being secured by such bone and/or softtissue-penetrating fixation devices or otherwise rigidly fixed to thefemur, artificial femoral bearing component, artificial tibial bearingcomponent or tibia and/or surrounding soft tissue. To that end, theouter body portion 108 of the prosthetic device 100 is shaped and sizedto prevent unwanted expulsion of the prosthetic device from the kneejoint. While bone must be removed to implant a femoral or tibial bearingcomponent, the meniscus prosthetic device is implanted into a patientwithout causing permanent damage to the patient's undamaged tibia orother bone and/or soft tissue structure(s) engaged by the prostheticdevice in some embodiments. In some instances the prosthetic device 100is implanted to alleviate the patient's knee problems while avoidingpermanent destruction of the patient's anatomy, such as cutting orreaming a large opening in the tibia. In such instances, the prostheticdevice 100 may be subsequently removed and replaced with anotherprosthetic device or treatment without adversely affecting thesubsequent treatment. In other instances where the femoral bearingsurface remains intact, a tibial bearing component may be implantedbefore placement of the prosthetic meniscus device.

To this end, the outer body portion 108 of the prosthetic deviceincludes a first portion 112 and a second portion or bridge 114. In someembodiments, the first portion 112 substantially matches the shape of anatural meniscus. In some embodiments, the outer body portion 108 has asemi-ellipsoidal shape. Accordingly, the first portion 112 extendsaround a majority of the outer body portion 108. The bridge 114 connectsthe two ends of the first portion 112. Thus, where the prosthetic deviceis configured for use as a medial meniscus device, the bridge 114extends along the lateral side of the device. Where the prostheticdevice is configured for use as a lateral meniscus device, the bridge114 extends along the medial side of the device. Accordingly, the outerbody portion 108—comprised of the first portion 112 and the bridge 114and having an increased thickness relative to the central body portion110—completely surrounds the central body portion 110 and serves tolimit movement of the prosthetic device after implantation. That is, theincreased height of the outer body portion 108 along with the contactpressure on the prosthetic device from being positioned between thefemoral component and the tibia prevents the prosthetic device frommoving outside of the desired range of positions within the knee joint.

The height or thickness of the bridge component 114 is based on the sizeof the femur notch and the distance to the cruciate ligaments in someembodiments. In some embodiments, the bridge 114 has a maximum height orthickness that is between ¼ and ¾ the maximum height or thickness of thefirst portion 112 of the outer body portion 108. In some embodiments,the size and shape of the bridge 114 is selected to achieve an optimalpressure distribution on the tibial plateau in order to mimic thepressure distribution of a healthy natural meniscus. The bridge 114 and,more generally, the outer body portion 108 are geometricallycharacterized by anterior, posterior, lateral-anterior, mid-lateral andlateral-posterior angles and heights as well as sagittal and coronalradii of curvature. Further, the outer body portion 108 and the centralbody portion 110 are shaped and sized such that the prosthetic device100 is self-centering. That is, the shape and size of the prostheticmeniscus device itself encourages the prosthetic device to position oralign itself with a desired orientation within the knee joint based onthe position of the prosthetic femoral bearing component. Accordingly,as the prosthetic meniscus device moves through a range of positionswithin the knee joint it naturally returns to the desired orientationdue to the shape and size of the outer and central body portion 108,110. In some embodiments, the outer body portion and, more specifically,the bridge 114 acts as a physical barrier limiting the movement of theprosthetic device caused by joint reaction forces. The shape of therelated femoral or tibial bearing component interacting with theself-centering or self-aligning mechanism combined with the prostheticdevice's ability to move within the knee joint results in improvedlocation of the prosthetic device 110 during typical gait cycles (e.g.,flexion-extension angles of 0° to 20° or “heel-strike” to “toe-off”).The result is that the prosthetic device 110 exhibits a load pressuredistribution similar to that of a natural meniscus.

The central body portion 110 defines an upper surface 116 and a lowersurface 118. The upper and lower surfaces 116, 118 are both loadedsurfaces. In particular, the upper and lower surfaces 116, 118 areconfigured to movingly engage with a prosthetic femoral bearing surfaceand a natural tibial plateau, respectively, or the inverse of a naturalfemoral bearing surface and an artificial tibial plateau, respectively.In that regard, the prosthetic device 110 can translate and rotate withrespect to the femur and/or tibia within a range. In some instances,translation is possible in both the anterior-posterior andmedial-lateral directions. In some embodiments, the upper surface 116includes both a vertical and horizontal surface. To that end, in someembodiments the upper surface 116 comprises a concave surface thatdefines the vertical and horizontal surfaces. The thickness of thecentral body portion 110 between the upper surface 116 and the lowersurface 118 supports stress distribution capability of the component,while the increased height of the upper surface 116 as it extendsoutwardly towards the outer body portion 108 defines the horizontalsurface of the component. Similarly, in some embodiments the lowersurface 118 includes both vertical and horizontal components. Inparticular, in some embodiments the lower surface 118 comprises a convexsurface. The thickness of the central body portion 110 between the uppersurface 116 and the lower surface 118 determines the load distributioncapacity of the component, while the tapered height of the lower surface116 as it extends outwardly towards the outer body portion 108 definesthe horizontal component. In some embodiments, the upper surface 116and/or the lower surface 118 are shaped such that the prosthetic device100 is biased towards a neutral position in the knee. For example, thearcuate profiles of the upper surface 116 and/or the lower surface 118are shaped such that the interaction between the surfaces and theprosthetic femoral component encourages the implant to a particularorientation relative to the surfaces. This allows the prosthetic device100 to be self-centering or self-aligning as discussed further below.

Referring to FIG. 7, shown therein is a diagrammatic cross-sectionalview of the prosthetic device 110 taken along an anterior to posteriorsection line between anterior end 113 and posterior end 115. The centralbody 110 is reinforced by pre-tensioned fibers 124 wound around the coreto inhibit outward deformation while allowing inward flexibility. Asshown, the anterior portion 113 of the outer body portion 108 has ananterior height or thickness 160. In that regard, the anterior height orthickness 160 of the anterior end 113 is between about 4 mm andimmediately adjacent bridge structure 114 could be as great as about 15mm and, in some instances, is between about 5.7 mm and about 9.3 mm. Inthe present embodiment, the anterior height or thickness 160 of theanterior end 113 is approximately 7.8 mm. In a smaller embodiment, theanterior height or thickness 160 is approximately 5.7 mm. In a largerembodiment, the anterior height or thickness 160 is approximately 9.3mm. The posterior height or thickness 162 of the posterior end 114 isbetween about 4 mm and immediately adjacent the bridge structure 114could be as great as about 20 mm and, in some instances, is betweenabout 7.7 mm and about 12.7 mm. In the present embodiment, the posteriorheight or thickness 162 of the posterior end 115 is approximately 9.0mm. In a smaller embodiment, the posterior height or thickness 162 isapproximately 7.7 mm. In a larger embodiment, the posterior height orthickness 162 is approximately 12.7 mm.

The anterior portion of the upper surface of the anterior portion 113has an anterior radius of curvature 164. In that regard, the anteriorradius of curvature 164 is between about 10 mm and about 100 mm and, insome instances, is between about 23.0 mm and about 33.1 mm. In thepresent embodiment, the radius of curvature 164 is approximately 72 mm.In another embodiment, the radius of curvature 164 is approximately 28mm. In a smaller embodiment, the radius of curvature 164 isapproximately 23 mm. In a larger embodiment, the radius of curvature 164is approximately 33.1 mm. The posterior portion of the upper surface ofthe posterior portion 115 has a posterior radius of curvature 166. Inthat regard, the posterior radius of curvature 166 is between about 5 mmand about 70 mm and, in some instances, is between about 15.2 mm andabout 24.2 mm. In the present embodiment, the radius of curvature 166 isapproximately 30 mm. In a smaller embodiment, the radius of curvature166 is approximately 15.2 mm. In a larger embodiment, the radius ofcurvature 166 is approximately 24.2 mm.

Further, the anterior portion 113 of the upper surface generally extendsat an anterior angle 168 with respect to an axis 170 extendingsubstantially perpendicular to a plane generally defined by theprosthetic device 100, as shown. The anterior angle 168 is between about45 degrees and about 75 degrees and, in some instances, is between about62 degrees and about 68 degrees. In the present embodiment, the angle168 is approximately 65 degrees. In a smaller embodiment, the angle 168is approximately 62 degrees. In a larger embodiment, the angle isapproximately 68 degrees. The posterior portion 115 of the upper surfacegenerally extends at an posterior angle 172 with respect to an axis 174extending substantially perpendicular to a plane generally defined bythe prosthetic device 100, as shown. The posterior angle 172 is betweenabout 35 degrees and about 70 degrees and, in some instances, is betweenabout 55 degrees and about 61 degrees. In the present embodiment, theangle 172 is approximately 58 degrees. In a smaller embodiment, theangle 172 is approximately 50 degrees. In a larger embodiment, the angle172 is approximately 65 degrees.

The central body portion 110 has a height or thickness 176 between theupper articulation surface 116 and the lower articulation surface 118.In some embodiments, the height or thickness 176 is the minimalthickness of the central body portion 110 and, in more specificembodiments, the minimal thickness of the entire prosthetic device 100.To that end, the height or thickness 176 is between about 1 mm and about3 mm and, in some instances, is between about 1.2 mm and about 2.1 mm.In the present embodiment, the height or thickness 176 is approximately1.5 mm. In a smaller embodiment, the height or thickness 176 isapproximately 1.2 mm. In a larger embodiment, the height or thickness176 is approximately 2.1 mm.

A variety of materials are suitable for use in making the prostheticdevices of the present disclosure. Medical grade polyurethane basedmaterials especially suitable for use in the embodiments describedinclude, but are not limited to, isolated or in combination, thefollowing:

Bionate®, manufactured by DSM, a polycarbonate-urethane is among themost extensively tested biomaterials ever developed. Carbonate linkagesadjacent to hydrocarbon groups give this family of materials oxidativestability, making these polymers attractive in applications whereoxidation is a potential mode of degradation, such as in pacemakerleads, ventricular assist devices, catheters, stents, and many otherbiomedical devices. Polycarbonate urethanes were the first biomedicalpolyurethanes promoted for their biostability. Bionate®polycarbonate-urethane is a thermoplastic elastomer formed as thereaction product of a hydroxyl terminated polycarbonate, an aromaticdiisocyanate, and a low molecular weight glycol used as a chainextender. The results of extensive testing encompassing Histology,Carcinogenicity, Biostability, and Tripartite Biocompatibility Guidancefor Medical Devices verifies the cost effective material'sbiocompatibility.

Another group of suitable materials are copolymers of silicone withpolyurethanes as exemplified by PurSil™, a Silicone Polyether Urethaneand CarboSil™, a Silicone Polycarbonate Urethane. Silicones have longbeen known to be biostable and biocompatible in most implants, and alsofrequently have the low hardness and low modulus useful for many deviceapplications. Conventional silicone elastomers can have very highultimate elongations, but only low to moderate tensile strengths.Consequently, the toughness of most biomedical silicone elastomers isnot particularly high. Another disadvantage of conventional siliconeelastomers in device manufacturing is the need for cross-linking todevelop useful properties. Once cross-linked, the resulting thermosetsilicone cannot be redissolved or remelted. In contrast, conventionalpolyurethane elastomers are generally thermoplastic with excellentphysical properties. Thermoplastic urethane elastomers (TPUs) combinehigh elongation and high tensile strength to form tough, albeit fairlyhigh-modulus elastomers. Aromatic polyether TPUs can have an excellentflex life, tensile strength exceeding 5000 psi, and ultimate elongationsgreater than 700 percent. These materials are often used forcontinuously flexing, chronic implants such as ventricular-assistdevices, intraaortic balloons, and artificial heart components. TPUs caneasily be processed by melting or dissolving the polymer to fabricate itinto useful shapes.

The prospect of combining the biocompatibility and biostability ofconventional silicone elastomers with the processability and toughnessof TPUs is an attractive approach to what would appear to be a nearlyideal biomaterial. For instance, in polycarbonate-based polyurethanes,silicone copolymerization has been shown to reduce hydrolyticdegradation of the carbonate linkage, whereas in polyether urethanes,the covalently bonded silicone seems to protect the polyether softsegment from oxidative degradation in vivo. DSM synthesizedsilicone-polyurethane copolymers by combining two previously reportedmethods: copolymerization of silicone (PSX) together with organic(non-silicone) soft segments into the polymer backbone, and the use ofsurface-modifying end groups to terminate the copolymer chains.

Other applicable materials include PurSil™ silicone-polyether-urethaneand CarboSil™ silicone-polycarbonate-urethane which are truethermoplastic copolymers containing silicone in the soft segment. Thesehigh-strength thermoplastic elastomers are prepared through a multi-stepbulk synthesis where polydimethylsiloxane (PSX) is incorporated into thepolymer soft segment with polytetramethyleneoxide (PTMO) (PurSil) or analiphatic, hydroxyl-terminated polycarbonate (CarboSil). The hardsegment consists of an aromatic diisocyanate, MDI, with low molecularweight glycol chain extender. The copolymer chains are then terminatedwith silicone (or other) Surface-Modifying End Groups. Aliphatic (AL)versions of these materials, with a hard segment synthesized from analiphatic diisocyanate, are also available.

Many of these silicone urethanes demonstrate desirable combinations ofphysical properties. For example, aromatic silicone polyetherurethaneshave a higher modulus at a given shore hardness than conventionalpolyether urethanes—the higher the silicone content, the higher themodulus (see PurSil Properties). Conversely, the aliphatic siliconepolyetherurethanes have a very low modulus and a high ultimateelongation typical of silicone homopolymers or even natural rubber (seePurSil AL Properties). These properties make these materials veryattractive as high-performance substitutes for conventional cross-linkedsilicone rubber. In both the PTMO and PC families, some polymers havetensile strengths three to five times higher than conventional siliconebiomaterials.

Further examples of suitable materials include Surface Modifying EndGroups (SMEs) which are surface-active oligomers covalently bonded tothe base polymer during synthesis. SMEs—which include silicone (S),sulfonate (SO), fluorocarbon (F), polyethylene oxide (P), andhydrocarbon (H) groups—control surface chemistry without compromisingthe bulk properties of the polymer. The result is that key surfaceproperties, such as thromboresistance, biostability, and abrasionresistance, are permanently enhanced without additional post-fabricationtreatments or topical coatings. This technology is applied to a widerange of DSM's polymers.

SMEs provide a series of base polymers that can achieve a desiredsurface chemistry without the use of additives. Polyurethanes preparedaccording to DSM's development process couple endgroups to the backbonepolymer during synthesis via a terminal isocyanate group, not a hardsegment. The added mobility of endgroups relative to the backbonefacilitates the formation of uniform overlayers by the surface-activeend blocks. The use of the surface active endgroups leaves the originalpolymer backbone intact so the polymer retains strength andprocessability. The fact that essentially all polymer chains carry thesurface-modifying moiety eliminates many of the potential problemsassociated with additives.

The SME approach also allows the incorporation of mixed endgroups into asingle polymer. For example, the combination of hydrophobic andhydrophilic endgroups gives the polymers amphipathic characteristics inwhich the hydrophobic versus hydrophilic balance may be easilycontrolled.

Other suitable materials, manufactured by CARDIOTECH CTE, includeChronoFlex® and Hydrothane™.

The ChronoFlex®, polycarbonate aromatic polyurethanes, family ofmedical-grade segmented biodurable polyurethane elastomers have beenspecifically developed by CardioTech International to overcome the invivo formation of stress-induced microfissures.

HydroThane™, hydrophilic thermoplastic polyurethanes, is a family ofsuper-absorbent, thermoplastic, polyurethane hydrogels ranging in watercontent from 5 to 25% by weight. HydroThane™ is offered as a clear resinin durometer hardness of 80 A and 93 Shore A. The outstandingcharacteristic of this family of materials is the ability to rapidlyabsorb water, high tensile strength, and high elongation. The result isa polymer having some lubricious characteristics, as well as beinginherently bacterial resistant due to their exceptionally high watercontent at the surface. HydroThane™ hydrophilic polyurethane resins arethermoplastic hydrogels, and can be extruded or molded by conventionalmeans. Traditional hydrogels on the other hand are thermosets anddifficult to process.

Additional suitable materials manufactured by THERMEDICS includeTecothante® (aromatic polyether-based polyurethane), Carbothane®(aliphatic polycarbonate-based polyurethane), Tecophilic® (high moistureabsorption aliphatic polyether-based polyurethane) and Tecoplast®(aromatic polyether-based polyurethane). Tecothane® is a family ofaromatic, polyether-based TPU's available over a wide range ofdurometers, colors, and radiopacifiers. One can expect Tecothane resinsto exhibit improved solvent resistance and biostability when comparedwith Tecoflex resins of equal durometers. Carbothane® is a family ofaliphatic, polycarbonate-based TPU's available over a wide range ofdurometers, colors and radiopacifiers. This type of TPU has beenreported to exhibit excellent oxidative stability, a property which mayequate to excellent long-term biostability. This family, like Tecoflex,is easy to process and does not yellow upon aging. Tecophilic® is afamily of aliphatic, polyether-based TPU's which have been speciallyformulated to absorb equilibrium water contents of up to 150% of theweight of dry resin.

Additional materials of interest include Tecogel, a new member to theTecophilic family, a hydrogel that can be formulated to absorbequilibrium water contents between 500% to 2000% of the weight of dryresin, and Tecoplast®, a family of aromatic, polyether-based TPU'sformulated to produce rugged injection molded components exhibiting highdurometers and heat deflection temperatures.

Additional potentially suitable materials include four families ofpolyurethanes, named Elast-Eon™, which are available from AorTechBiomaterials.

Elast-Eon™ 1, a Polyhexamethylene oxide (PFMO), aromatic polyurethane,is an improvement on conventional polyurethane in that it has a reducednumber of the susceptible chemical groups. Elast-Eon™ 2, a Siloxanebased macrodiol, aromatic polyurethane, incorporates siloxane unto thesoft segment. Elast-Eon™ 3, a Siloxane based macrodiol, modified hardsegment, aromatic polyurethane, is a variation of Elast-Eon™ 2 withfurther enhanced flexibility due to incorporation of siloxane into thehard segment. Elast-Eon™ 4 is a modified aromatic hard segmentpolyurethane.

Bayer Corporation also produces candidate materials. Texin 4210 andTexin 4215 are thermoplastic polyurethane/polycarbonate blends forinjection molding and extrusion. Texin 5250, 5286 and 5290 are aromaticpolyether-based medical grade materials with Shore D hardness ofapproximately 50, 86, and 90 respectively for injection molding andextrusion.

In some embodiments, the prosthetic device is a melt mold compositeimplant composed of two biocompatible materials: DSM Bionate®Polycarbonate-Urethane (PCU), 80 Shore A, matrix material and ultra highmolecular weight polyethylene (UHMWPE) reinforcement material (DyneemaPurity). In some particular embodiments, a prosthetic device formed ofPCU and reinforced circumferentially with DSM Dyneema® fibers results ina desirable distribution of loads on the underlying articulationsurfaces of the prosthetic device.

Referring now to FIG. 8, there is shown a top view of a knee joint withan injured meniscus 10. The meniscus includes an outer rim 15 that isanchored to the bone along the posterior rim 20 and the anterior rim 22.Referring to FIG. 8, the torn segments along with the undamaged centralmeniscus have been removed to expose the underlying tibia and define animplantation area 30. The implantation area 30 is bounded by sidewall21. A prosthetic meniscus device 110 according to one aspect of thecurrent disclosure is positioned in the meniscus pocket 30 defined bythe sidewall 21. As will be explained in greater detail below, theprosthetic meniscus engages an artificial femoral bearing component tomove the meniscus device into positions A, B and C within the meniscuspocket 30. In that regard, the positions A, B, and C can belongitudinally, rotationally, and/or laterally offset from one another.

Referring now to FIGS. 9A-9C, there is shown an artificial femoralbearing component (FBC) 120 implanted on a femur F and a prostheticmeniscus device (PMD) 110 positioned between the femoral bearingcomponent and the natural tibial plateau of the tibia T. With the axisof the femur FA aligned with the axis of the tibia TA, a first bearingportion of the FBC engages the PMD and the PMD is positioned in a firstposition A with respect to the tibia. The position of the PMD 110 can becharacterized by a superior-inferior axis MP extending through themidpoint of the PMD. In position A, the PMD is offset from the tibialaxis TA by distance D1. Distance D1 describes the separation between theaxis MP of the PMD and the tibial axis TA. FIG. 10A illustrates the viewfrom the tibia in position A and shows the rotational orientation of thePMD sidewall 114 in relation to the anterior-posterior axis AP, as wellas the orientation of the PMD 110 to the axis FB extending from theanterior to the posterior of the FBC 120. In position A, the anglebetween the edge of the PMD 120 and the axis AP is β.

Referring now to FIGS. 9B and 10B, these figures illustrate the movementof the PMD as the femur F is moved to the position of the angle α′between axis FA and axis TA. The PMD is now engaged with a secondbearing surface of the FBC having a different radius of curvature. As aresult of this contact, the PMD 110 has translated posteriorly and isnow spaced a distance D1′ from the axis TA, which is greater than D1.Additionally, the PMD 110 has rotated clockwise with respect to axis APto smaller angle β′. The illustrated relationship is position B. The PMD110 has moved longitudinally, rotationally, and/or laterally betweenpositions A and B. Translation of the PMD 110 along the axis AP can bedescribed as longitudinal movement. Translation of the PMD 110 along amedial-lateral axis perpendicular to the axis AP can be described aslateral movement.

Referring now to FIGS. 9C and 10C, continued rotation of the femur withrespect to the tibia results in angle α″ which is greater than angle α′and almost 90 degrees. The PMD is now engaged with a third bearingsurface of the FBC having a different radius of curvature. As a resultof this contact, the PMD 110 has translated posteriorly and is nowspaced a distance D1″ from the axis TA, which is greater than D1′.Additionally, the PMD 110 has rotated clockwise with respect to axis APto smaller angle β″ which now a negative angle in comparison to the APaxis. The illustrated relationship is position C. The PMD 110 has movedlongitudinally, rotationally, and/or laterally between positions B andC, and positions A and C.

While the foregoing are not limiting, the PMD total translation distanceD1 can range from 3-20 mm in the anterior to posterior plane, with oneembodiment having D1 of 5 mm, D1′ of 10 mm and D1″ of 15 mm. Similarly,the PMD rotational angle can range, without limitation, from 3 to 30degrees of total angular rotation. With respect to the embodiment shownin FIGS. 10A-10C, β is approximately 10 degrees, β′ is approximately 5degrees, and β″ is approximately −5 degrees from the AP line. Althoughthe angles are shown with respect to the AP line, the sidewall 114 alsovaries by the same angular amounts from the axis FB of the FBC 120.

As shown above with respect to FIGS. 9A-10C, as the first, second andthird regions of the FBC engage the PMD, the PMD is floating on thenatural tibial plateau and translates while simultaneously rotating intothe positions shown. In one form, the first bearing surface of the FBCengages a first meniscus bearing surface on the PMD to force the device110 into position A, while a second bearing surface on the FBC engages asecond meniscus bearing surface on the PMD to force the device intoposition B, while a third bearing surface on the FBC engages a thirdmeniscus bearing surface on the PMD to force the device into position C.

Referring now to FIGS. 11A and 11B, there is shown a further embodimentof a meniscus replacement device 460 according to another aspect of thepresent disclosure. The implant 460 includes tethering loops 450, 454,456 and 458. As explained more fully in U.S. application Ser. No.14/212,330 filed Mar. 14, 2014 entitled “Meniscus Prosthetic Deviceswith Anti-Migration or Radiopaque Features”, incorporated by referenceherein in its entirety, the loops are formed by a series of fibersloosely wound around a core after the tension elements are positioned,with slack portions held outwardly during the over-flow molding processto form the loops. Thus, in one form, the loops 450, 454, 456 and 458are formed of a series of filaments that are partially embedded withinthe over molded area and partially extending beyond the sidewalls. Theloops themselves may also include a coating of the over moldingmaterial. In one form, each loop has a unique set of filaments extendingaround the core such that if one loop is cut off, severing of the fiberswill not impact the remaining loops. In still a further form, one ormore fiber reinforced tabs extend outwardly from the outer side wall.Although the tabs lack a preformed opening, the tabs provide fiberreinforced areas for the passage of a needle and suture that can firmlyretain the suture without damaging the pliable material of the implant.In one aspect, the tabs are spaced around the implant at strategiclocations, while in another form, the fiber reinforced tab extendscompletely around the side wall perimeter of the implant.

In use, the implant 460 can be inserted into the joint space afterimplantation of the femoral bearing component 120. In one aspect, theanterior tethering loop 458 is positioned adjacent the anterior rim 22and a suture 470 is passed through the loop 458 and the anterior rim 22.The tension applied to the suture can be varied to provide the correctamount of freedom of movement within the joint space. The other tetherloops that are not used can be severed by the physician beforeimplantation in the joint space. In an alternative placement, theimplant 460 is positioned in the spaced formed within the remainingportions of the meniscus 15 with the tethering loop 456 positionedadjacent the posterior rim 20. A suture is passed through the loop 456and the posterior rim 20 to maintain the implant within the joint space.In both the described tethering arrangements, the implant 460 has a highdegree of freedom of movement with the joint space such that the implantretains its ability to float freely within the joint to mimic a naturalmeniscus. In still a further aspect, the one or more tether loops 454,456 and 458 are attached to the soft tissue of the joint capsule.

Referring now to FIG. 11B, the implant 460 is more fully tethered in thejoint space by a suture that extends through all or part of the tetherloops 454, 456 and 458 and around the meniscus rim 15 including theposterior rim 20 and the anterior rim 22. In this arrangement, theimplant 460 is constrained to a more limited zone of movement providinga limited range of motion, although it is permitted to translateanterior to posterior, and to rotate with respect to the tibial plateau.

Referring now to FIGS. 12A-13C, there is shown a further form of apartial unicompartmental knee replacement system according to anotheraspect of the present disclosure. The PUKR 1200 includes a prostheticmeniscus device (PMD) 1210 and an artificial tibial bearing component1220. In that regard, the PMD 1210 is disposed between and in contactwith the artificial tibial bearing component 1220 and the naturalfemoral bearing surface. The upper surface of the PMD 1210 is shapedgenerally as described above with a meniscus bearing surface configuredto engage a first, second and third bearing surface of the femur. Asalso described above, the first, second, and third bearing surfaces ofthe natural femur can have respective first, second, and third radii ofcurvature. The lower surface of the PMD 1210 is shaped to engage the TBC1220 and move the PMD through a variety of positions as explained below.

As shown in FIGS. 14A-15C, the tibial bearing component includes a keel1240, having a height H1, for positioning in a bone channel in the tibiato anchor the device in a stationary position with respect to the tibia.The TBC includes a medial side wall 1228 and a peak 1224 defining themaximum height H2. The TBC has a maximum width of W and length of L. Inone embodiment, H1 is approximately 8 mm, H2 is approximately 14 mm, Wis approximately 31 mm and L is approximately 49 mm. A bearing surface1226 extends between sidewalls 1228 and 1230, and end walls 1232 and1234. The bearing surface 1226 includes a convex region adjacent peak1224.

Referring now to FIGS. 16A-17C, there is shown a series of angularpositions of the femur in relation to the tibia and the correspondingmovement of the PUKR system in the knee joint. In FIG. 16A, femoral axisFA is substantially aligned with the tibial axis TA. In this position,A, the posterior wall 1212 of the PMD 1210 is substantially aligned withthe posterior wall 1250 of the TBC 1220. With the axis of the femur FAaligned with the axis of the tibia TA, a first bearing portion of theTBC engages the PMD and the PMD is positioned in a first position A withrespect to the tibia. FIG. 17A illustrates the view from the femur inposition A and shows the rotational orientation of the PMD in relationto the sidewall 1228 of the TBC shown by the line TP, as well as theorientation of the PMD to the tibia. The line TP represents ananterior-posterior axis along the sidewall 1228 of the TBC 1220. Inposition A, the angle between the medial edge of the PMD 1210 and theline TP is A.

Referring now to FIGS. 16B and 17B, these figures illustrate themovement of the PMD 1210 as the femur F is moved to the position of theangle α′ between axis FA and axis TA. The PMD 1210 is now engaged with asecond bearing surface of the natural femur having a different radius ofcurvature causing the PMD to engage the TBC bearing surface 1226resulting in translation and rotation of the PMD as shown in FIGS. 16Band 17B. As a result of this contact, the PMD 110 has translatedposteriorly and now has its posterior wall 1212 spaced a distance D2′from the posterior wall 1250 of the TBC 1220. Additionally, the PMD 1210has rotated clockwise with respect to line TP to smaller angle A′. Theillustrated relationship is position B. The PMD 110 has movedlongitudinally, rotationally, and/or laterally between positions A andB.

Referring now to FIGS. 16C and 17C, continued rotation of the femur withrespect to the tibia results in angle α″ which is greater than angle α′.The PMD is now engaged with a third bearing surface of the natural femurhaving a different radius of curvature and a different portion of theTBC bearing surface 1226. As a result of this contact, the PMD 110 hastranslated posteriorly and is now spaced a distance D2″ from theposterior surface 1250, which is greater than D2′. Additionally, the PMD110 has rotated clockwise with respect to sidewall 1228 of the TBCrepresented by line TP to smaller angle A″ which now a negative angle incomparison to the TP line. The illustrated relationship is position C.The PMD 110 has moved longitudinally, rotationally, and/or laterallybetween positions B and C, and positions A and C.

FIG. 16D illustrates that continued rotation of the femur with respectto the tibia to angle α′″, which is substantially 90 degrees, results infurther translation to a distance D2′ which is greater than D2″.

While the foregoing are not limiting, the PMD total translation distanceD2 can range from 3-20 mm in the anterior to posterior plane, with oneembodiment having D2′ of 3 mm, D2″ of 7 mm and D2′″ of 14 mm. Similarly,the PMD rotational angle can range, without limitation, from 3 to 30degrees of total angular rotation. With respect to the embodiment shownin FIGS. 10A-10C, angle A is approximately 10 degrees, angle A′ isapproximately 3 degrees, and angle A″ is approximately −10 degrees fromthe TP line.

Although described in the context of a partial unicompartmental kneereplacement system, the composite implants described above may beutilized for forming a variety of prosthetic devices. For example, insome instances the composite implants are utilized for knee joints(including meniscus and total knee joints), hip joints (includingacetabular cups), shoulder joints, elbow joints, finger joints, andother load and/or non-load receiving prosthetic devices.

It should be appreciated that in some instances the prosthetic devicesof the present disclosure are formed by other processes than thosedescribed herein. These manufacturing processes include any suitablemanufacturing method. For example, without limitation any of thefollowing manufacturing methods may be utilized: injection moldingincluding inserting inserts; compression molding including insertinginserts; injection-compression molding including inserting inserts;compression molding of prefabricated elements pre-formed by any of theabove methods including inserting inserts; spraying including insertinginserts; dipping including inserting inserts; machining from stocks orrods; machining from prefabricated elements including inserting inserts;and/or any of the above methods without inserts. Further, it should beappreciated that in some embodiments the prosthetic devices of thepresent disclosure are formed of medical grade materials other thanthose specifically identified above. In that regard, in some embodimentsthe prosthetic devices are formed of any suitable medical gradematerial.

While the principles of the present disclosure have been set forth usingthe specific embodiments discussed above, no limitations should beimplied thereby. Any and all alterations or modifications to thedescribed devices, instruments, and/or methods, as well as any furtherapplication of the principles of the present disclosure that would beapparent to one skilled in the art are encompassed by the presentdisclosure even if not explicitly discussed herein. It is alsorecognized that various presently unforeseen or unanticipatedalternatives, modifications, and variations of the present disclosuremay be subsequently made by those skilled in the art. All suchvariations, modifications, and improvements that would be apparent toone skilled in the art to which the present disclosure relates areencompassed by the following claims.

What is claimed is:
 1. A partial unicompartmental knee replacementsystem for implantation between a femur and a tibia of a patient,comprising: a femoral component configured for resurfacing at least aportion of a femoral condyle, the femoral component having a first areawith a first radius of curvature, a second area with a second radius ofcurvature and a third area with a third radius of curvature; and ameniscus component, configured for placement between the femoralcomponent and the natural tibia, wherein the meniscus component floatsin the knee joint between the tibia and the femoral component and has afirst position in the knee joint when in contact with the first area, asecond position in the knee joint when in contact with the second areaand a third position in the knee joint when in contact with the thirdarea.
 2. The system of claim 1, wherein the first position isrotationally offset from at least one of the second and third positions.3. The system of claim 1, wherein the first position is longitudinallyoffset from at least one of the second and third positions.
 4. Thesystem of claim 1, wherein the first position is laterally offset fromat least one of the second and third positions.
 5. The system of claim1, wherein rotation of the meniscus component is greater than 2.5degrees.
 6. The system of claim 1, wherein translation of the meniscuscomponent is greater than 5 mm.
 7. The system of claim 1, wherein themeniscus component loosely attached to soft tissue adjacent the kneejoint.
 8. The system of claim 1, wherein at least the first radius ofcurvature is different than the third radius of curvature.
 9. The systemof claim 5, wherein the translation of the meniscus is greater than 5mm.
 10. A partial unicompartmental knee replacement system forimplantation between a femur and a tibia of a patient, the systemcomprising: a tibial bearing component having an anchoring surface forsecured fastening to the tibial bone and an opposing bearing surfacehaving a central convex surface adjacent a medial side wall; a flexiblemeniscus component having a femoral bearing surface configured toarticulate with the cartilage bearing surface on the femur and anopposing tibial bearing surface configured to selectively engage thetibial bearing surface such that in a first position relative to thetibial bearing component, the meniscus component has a first angularposition relative to the medial side wall and in a second positionrelative to the tibial bearing component, translated posteriorly fromthe first position, the meniscus component has a second angular positionrelative to the medial side wall, the second position being differentthan the first position.
 11. The system of claim 10, wherein rotation ofthe meniscus component between the first and second angular positions isgreater than 3 degrees.
 12. The system of claim 10, wherein translationof the meniscus component between the first and second positions isgreater than 3 mm.
 13. The system of claim 10, wherein the meniscuscomponent has a third position relative to the tibial bearing component,the third position translated posteriorly from at least one of the firstand second positions, and wherein, in the third position, the meniscuscomponent has a third angular position relative to the medial side wall,the third position being different than at least one of the first andsecond positions.
 14. A method of inserting a unicompartmental kneereplacement system between a femur and a tibia of a patient, the methodcomprising: implanting on a femoral condyle a femoral component havingat least two different radii along its contact surface; and inserting ameniscal component between the tibia and femoral component, the meniscalcomponent retained by engagement between the femoral component and thenatural bearing surface of the tibia.
 15. The method of claim 14,wherein inserting a meniscal component includes: positioning themeniscal component between the tibia and femoral component such that themeniscal component floats between the femoral component and the naturalbearing surface of the tibia.
 16. The method of claim 14, whereininserting a meniscal component includes: positioning the meniscalcomponent between the tibia and femoral component such that the meniscalcomponent has a first position when in contact with a first area of thefemoral component having a first radius of curvature and a secondposition when in contact with a second area of the femoral componenthaving a second radius of curvature.
 17. The method of claim 16, whereinthe first position and the second position are at least one ofrotationally offset, longitudinally offset, and laterally offset. 18.The method of claim 16, wherein the meniscal component has a thirdposition when in contact with a third area of the femoral componenthaving a third radius of curvature, and wherein the third position is atleast one of rotationally offset, longitudinally offset, and laterallyoffset from at least one of the first and second positions.